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Topic: water seperation  (Read 13171 times)

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singerp

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water seperation
« on: June 05, 2004, 09:05:06 PM »

 Stupid question. How do you seperate the hydrogen and oxygen in water into their seperate flammable gases? If you can,the exact process. Not a homework question.

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Re:water seperation
« Reply #1 on: June 05, 2004, 11:16:20 PM »
It's simple electrolysis.  Just put an electrical current through some water and hydrogen will form at the negative electrode and oxygen will form at the positive electrode.  The electrical current provides the energy needed to break the hydrogen-oxygen bonds and also provides the electrons needed for those atoms to bond with themselves, thus forming hydrogen and oxygen gas.  This process, however, proceeds fairly slowly unless a salt is added to the water to increase its conductivity.  However, adding sodium chloride causes some chlorine gas to form with the oxygen and some sodium hydroxide to form in the solution.  
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Re:water seperation
« Reply #2 on: June 05, 2004, 11:42:47 PM »
However, adding sodium chloride causes some chlorine gas to form with the oxygen and some sodium hydroxide to form in the solution.  

I dont think that adding some NaCl will lead to the formation of chlorine gas. Aq anions discharge preferentially according to their concentration. In a diluted NaCl solution, it is most unlikely that the chloride anion will be discharged to form chlorine gas. Instead, the hydroxide ion will be discharged preferentially to give oxygen gas according to this equation:

4OH- => 2H2O + O2 + 4e

I disagree that there will be aq NaOH due to discharge of hydroxide ions at the anode.
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chemicalLindsay

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Re:water seperation
« Reply #3 on: June 06, 2004, 02:09:19 AM »
Ive done it before and geodome is right no chlorine gas will be discharged unless the solution is concentrated because if you make a concentrated solution of sodium chloride there will be more chlorine ions present in the solution than hydroxide and so therefore chlorine gas will be discharged.My main suggestions are to use good graphite electrodes (note graphite is pencil lead ,however the real electrodes are the best) and have a good consistant power source that has both a good amperage output and a good voltage output (note two nine volt batteries seemed to work well for our science teacher).also  oxygen isn't a flammable gas it is just what combines with a fuel or hydrogen to burn or explode.If it was flammable imagine what would happen when you lit a match.

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Re:water seperation
« Reply #4 on: June 07, 2004, 03:17:41 PM »
I've done concentrated NaCl electrolysis. Chlorine gas was produces and NaOH solid was formed.
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Offline AWK

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Re:water seperation
« Reply #5 on: June 08, 2004, 04:01:06 AM »
How do you seperate the hydrogen and oxygen in water into their seperate flammable gases?
Only hydrogen is a flamable gas.

In industrial elecrolysis always solution of KOH (or NaOH) is used
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Offline cliverlong

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Re:water seperation (sic)
« Reply #6 on: November 03, 2009, 04:51:24 AM »
However, adding sodium chloride causes some chlorine gas to form with the oxygen and some sodium hydroxide to form in the solution.  

I dont think that adding some NaCl will lead to the formation of chlorine gas. Aq anions discharge preferentially according to their concentration. In a diluted NaCl solution, it is most unlikely that the chloride anion will be discharged to form chlorine gas. Instead, the hydroxide ion will be discharged preferentially to give oxygen gas according to this equation:

4OH- => 2H2O + O2 + 4e

I disagree that there will be aq NaOH due to discharge of hydroxide ions at the anode.
Hello

Does anyone have a link to a dcoument that succinctly describes:

The effect of concentration on what is discharged during aqueous electrolysis?
Which anions are discharged during electrolysis? For example in electrolysis conc. or dilute sulphuric acid or conc. vs dil. hydrochloric acid?
Is (standard) electrode potential relevant in deciding products of aqueous electrolysis at different concentrations?

A reference to a textbook that I can get from the library will be fine.

I have read lists of the products in various books and web sites over the years but precious few explanations.

Thanks

Clive

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Re: water seperation
« Reply #7 on: November 03, 2009, 08:31:33 AM »
First and the most important - Nernst equation. That's where the standard potentials and concentrations enter the scene.

Then it becomes more complicated, as there are details (overpotential on different electrodes) that can be determined only experimentally... Sorry, no links nor books.
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